drm/vc4: don't check if plane->state->fb == state->fb #5832
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Currently, when using non-blocking commits, we can see the following kernel warning: [ 110.908514] ------------[ cut here ]------------ [ 110.908529] refcount_t: underflow; use-after-free. [ 110.908620] WARNING: CPU: 0 PID: 1866 at lib/refcount.c:87 refcount_dec_not_one+0xb8/0xc0 [ 110.908664] Modules linked in: rfcomm snd_seq_dummy snd_hrtimer snd_seq snd_seq_device cmac algif_hash aes_arm64 aes_generic algif_skcipher af_alg bnep hid_logitech_hidpp vc4 brcmfmac hci_uart btbcm brcmutil bluetooth snd_soc_hdmi_codec cfg80211 cec drm_display_helper drm_dma_helper drm_kms_helper snd_soc_core snd_compress snd_pcm_dmaengine fb_sys_fops sysimgblt syscopyarea sysfillrect raspberrypi_hwmon ecdh_generic ecc rfkill libaes i2c_bcm2835 binfmt_misc joydev snd_bcm2835(C) bcm2835_codec(C) bcm2835_isp(C) v4l2_mem2mem videobuf2_dma_contig snd_pcm bcm2835_v4l2(C) raspberrypi_gpiomem bcm2835_mmal_vchiq(C) videobuf2_v4l2 snd_timer videobuf2_vmalloc videobuf2_memops videobuf2_common snd videodev vc_sm_cma(C) mc hid_logitech_dj uio_pdrv_genirq uio i2c_dev drm fuse dm_mod drm_panel_orientation_quirks backlight ip_tables x_tables ipv6 [ 110.909086] CPU: 0 PID: 1866 Comm: kodi.bin Tainted: G C 6.1.66-v8+ raspberrypi#32 [ 110.909104] Hardware name: Raspberry Pi 3 Model B Rev 1.2 (DT) [ 110.909114] pstate: 60000005 (nZCv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--) [ 110.909132] pc : refcount_dec_not_one+0xb8/0xc0 [ 110.909152] lr : refcount_dec_not_one+0xb4/0xc0 [ 110.909170] sp : ffffffc00913b9c0 [ 110.909177] x29: ffffffc00913b9c0 x28: 000000556969bbb0 x27: 000000556990df60 [ 110.909205] x26: 0000000000000002 x25: 0000000000000004 x24: ffffff8004448480 [ 110.909230] x23: ffffff800570b500 x22: ffffff802e03a7bc x21: ffffffecfca68c78 [ 110.909257] x20: ffffff8002b42000 x19: ffffff802e03a600 x18: 0000000000000000 [ 110.909283] x17: 0000000000000011 x16: ffffffffffffffff x15: 0000000000000004 [ 110.909308] x14: 0000000000000fff x13: ffffffed577e47e0 x12: 0000000000000003 [ 110.909333] x11: 0000000000000000 x10: 0000000000000027 x9 : c912d0d083728c00 [ 110.909359] x8 : c912d0d083728c00 x7 : 65646e75203a745f x6 : 746e756f63666572 [ 110.909384] x5 : ffffffed579f62ee x4 : ffffffed579eb01e x3 : 0000000000000000 [ 110.909409] x2 : 0000000000000000 x1 : ffffffc00913b750 x0 : 0000000000000001 [ 110.909434] Call trace: [ 110.909441] refcount_dec_not_one+0xb8/0xc0 [ 110.909461] vc4_bo_dec_usecnt+0x4c/0x1b0 [vc4] [ 110.909903] vc4_cleanup_fb+0x44/0x50 [vc4] [ 110.910315] drm_atomic_helper_cleanup_planes+0x88/0xa4 [drm_kms_helper] [ 110.910669] vc4_atomic_commit_tail+0x390/0x9dc [vc4] [ 110.911079] commit_tail+0xb0/0x164 [drm_kms_helper] [ 110.911397] drm_atomic_helper_commit+0x1d0/0x1f0 [drm_kms_helper] [ 110.911716] drm_atomic_commit+0xb0/0xdc [drm] [ 110.912569] drm_mode_atomic_ioctl+0x348/0x4b8 [drm] [ 110.913330] drm_ioctl_kernel+0xec/0x15c [drm] [ 110.914091] drm_ioctl+0x24c/0x3b0 [drm] [ 110.914850] __arm64_sys_ioctl+0x9c/0xd4 [ 110.914873] invoke_syscall+0x4c/0x114 [ 110.914897] el0_svc_common+0xd0/0x118 [ 110.914917] do_el0_svc+0x38/0xd0 [ 110.914936] el0_svc+0x30/0x8c [ 110.914958] el0t_64_sync_handler+0x84/0xf0 [ 110.914979] el0t_64_sync+0x18c/0x190 [ 110.914996] ---[ end trace 0000000000000000 ]--- This happens because, although `prepare_fb` and `cleanup_fb` are perfectly balanced, we cannot guarantee consistency in the check plane->state->fb == state->fb. This means that sometimes we can increase the refcount in `prepare_fb` and don't decrease it in `cleanup_fb`. The opposite can also be true. In fact, the struct drm_plane .state shouldn't be accessed directly but instead, the `drm_atomic_get_new_plane_state()` helper function should be used. So, we could stick to this check, but using `drm_atomic_get_new_plane_state()`. But actually, this check is not really needed. We can increase and decrease the refcount symmetrically without problems. This is going to make the code more simple and consistent. Signed-off-by: Maíra Canal <[email protected]>
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Thanks - this fixed the issue I was seeing (a master build of kodi with fences enabled producing the quoted kernel splat on Pi3). |
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kernel: ARM: dts: bcm2712-rpi-5-b: Add eth_ledx parameters See: raspberrypi/linux#5826 kernel: ARM: dts: bcm2712-rpi-5-b: Add fan speed dtparams See: raspberrypi/linux#5822 kernel: drm/vc4: don't check if plane->state->fb == state->fb See: raspberrypi/linux#5832 kernel: spi: bcm2835: Support spi0-0cs and SPI_NO_CS mode See: raspberrypi/linux#5837 kernel: Add link freq Control for IMX519 and Arducam64MP See: raspberrypi/linux#5841 kernel: watchdog: bcm2835_wdt: Fix WDIOC_SETTIMEOUT handling See: raspberrypi/linux#5838
popcornmix
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Jan 10, 2024
kernel: ARM: dts: bcm2712-rpi-5-b: Add eth_ledx parameters See: raspberrypi/linux#5826 kernel: ARM: dts: bcm2712-rpi-5-b: Add fan speed dtparams See: raspberrypi/linux#5822 kernel: drm/vc4: don't check if plane->state->fb == state->fb See: raspberrypi/linux#5832 kernel: spi: bcm2835: Support spi0-0cs and SPI_NO_CS mode See: raspberrypi/linux#5837 kernel: Add link freq Control for IMX519 and Arducam64MP See: raspberrypi/linux#5841 kernel: watchdog: bcm2835_wdt: Fix WDIOC_SETTIMEOUT handling See: raspberrypi/linux#5838
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Currently, when using non-blocking commits, we can see the following kernel warning:
This happens because, although
prepare_fbandcleanup_fbare perfectly balanced, we cannot guarantee consistency in the check plane->state->fb == state->fb. This means that sometimes we can increase the refcount inprepare_fband don't decrease it incleanup_fb. The opposite can also be true.In fact, the struct drm_plane .state shouldn't be accessed directly but instead, the
drm_atomic_get_new_plane_state()helper function should be used. So, we could stick to this check, but usingdrm_atomic_get_new_plane_state(). But actually, this check is not really needed. We can increase and decrease the refcount symmetrically without problems.This is going to make the code more simple and consistent.
This patch addresses issue #5730. I also sent this patch upstream [1].
[1] https://lore.kernel.org/dri-devel/[email protected]/T/